Participants in both groups will receive 7.5 µg/kg G-CSF twice daily (morning and evening) for 4 days. In the evening (approximately 10:00 pm) on Day 4, a dose of plerixafor (240 µg/kg) will be administered. Apheresis will be initiated the next morning, approximately 10 to 11 hours after plerixafor is given. Participants will continue to receive G-CSF twice daily and to receive the evening dose of plerixafor followed by apheresis the next morning for up to a total of 4 aphereses or until ≥5*10^6 CD34+ cells/kg are collected.